MiniZip.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.IO.Compression;
using System.Text;

namespace ModUpdater
{
    public static class MiniZip
    {
        public struct ZipEntry
        {
            public string FileName;
            public byte[] Data;
        }

        public static List<ZipEntry> Extract(byte[] zipBytes)
        {
            var entries = new List<ZipEntry>();

            using (var stream = new MemoryStream(zipBytes))
            using (var reader = new BinaryReader(stream))
            {
                while (stream.Position < stream.Length - 4)
                {
                    uint signature = reader.ReadUInt32();
                    if (signature != 0x04034b50)
                        break;

                    reader.ReadUInt16(); // version needed
                    ushort flags = reader.ReadUInt16();
                    ushort method = reader.ReadUInt16();
                    reader.ReadUInt32(); // mod time + date
                    reader.ReadUInt32(); // crc32
                    uint compressedSize = reader.ReadUInt32();
                    uint uncompressedSize = reader.ReadUInt32();
                    ushort nameLen = reader.ReadUInt16();
                    ushort extraLen = reader.ReadUInt16();

                    string fileName = Encoding.UTF8.GetString(reader.ReadBytes(nameLen));
                    reader.ReadBytes(extraLen);

                    bool hasDataDescriptor = (flags & 0x08) != 0;

                    if (fileName.EndsWith("/") || fileName.EndsWith("\\"))
                    {
                        if (compressedSize > 0)
                            reader.ReadBytes((int)compressedSize);
                        continue;
                    }

                    byte[] fileData;

                    if (method == 0)
                    {
                        fileData = reader.ReadBytes((int)compressedSize);
                    }
                    else if (method == 8)
                    {
                        byte[] compressed = reader.ReadBytes((int)compressedSize);
                        using (var compStream = new MemoryStream(compressed))
                        using (var deflate = new DeflateStream(compStream, CompressionMode.Decompress))
                        using (var output = new MemoryStream())
                        {
                            deflate.CopyTo(output);
                            fileData = output.ToArray();
                        }
                    }
                    else
                    {
                        throw new NotSupportedException($"Unsupported compression method {method} for {fileName}");
                    }

                    if (hasDataDescriptor)
                    {
                        uint maybeSignature = reader.ReadUInt32();
                        if (maybeSignature == 0x08074b50)
                        {
                            reader.ReadBytes(12); // crc32 + compressed + uncompressed
                        }
                        else
                        {
                            reader.ReadBytes(8); // compressed + uncompressed (maybeSignature was crc32)
                        }
                    }

                    entries.Add(new ZipEntry { FileName = fileName, Data = fileData });
                }
            }

            return entries;
        }
    }
}